1. Field of the Invention
The present invention relates to a method of managing a queuing operation for a wireless communications system and related communications device, and more particularly to a method of managing a queuing operation corresponding to a cell update procedure in a wireless communications system and related communications device.
2. Description of the Prior Art
The third generation (3G) mobile communications system has adopted a Wideband Code Division Multiple Access (WCDMA) wireless air interface access method for a cellular network. WCDMA can provide high frequency spectrum utilization, universal coverage, and high quality, high speed multimedia data transmission. The WCDMA method also meets all kinds of QoS requirements simultaneously, providing diverse flexible two-way transmission services and better communication quality to reduce transmission interruption rates.
For the universal mobile telecommunications system (UMTS), the 3G communications system comprises User Equipment (UE), the UMTS Terrestrial Radio Access Network (UTRAN), and the Core Network (CN). Communications protocols utilized include Access Stratum (AS) and Non-Access Stratum (NAS). AS comprises various sub-layers for different functions, including Radio Resource Control (RRC), Radio Link Control (RLC), Media Access Control (MAC), Packet Data Convergence Protocol (PDCP), and Broadcast/Multicast Control (BMC). The sub-layers mentioned, and their operating principles, are well known in the art, and detailed description thereof is omitted.
RRC is a Layer 3 communications protocol, and is the core of the AS communications protocol. All radio resource information exchange, radio resource configuration control, QoS control, channel transmission format configuration control, packet segmentation/concatenation processing and control, and NAS protocol transmission processing is performed by the RRC layer. Between the user end and the network end, the RRC layer exchanges RRC Messages, also known as signaling, through RRC procedures. RRC Messages are formed from many Information Elements (IE) used for embedding necessary information for setting, changing, or releasing protocol entities of Layer 2 (RLC, MAC) and Layer 1 (Physical Layer), thereby establishing, adjusting, or canceling information exchange channels to perform data packet transportation.
According to the RRC protocol specification developed by the 3rd Generation Partnership Project (3GPP), the RRC procedures include a cell update procedure, which is initiated by the UE in response to certain events in UE e.g. uplink data transmission, paging response, or cell reselection. The RRC message exchange in the cell update procedure includes a CELL UPDATE message transmitted from the UE to the UTRAN, and a CELL UPDATE CONFIRM message transmitted from the UTRAN to the UE. According to content of the CELL UPDATE CONFIRM message, the UE performs radio bearer reconfiguration or release, mobile information update, or transport channel reconfiguration, etc.
During the cell update procedure, the UTRAN can utilize a queuing operation to queue the UE when the current serving frequency carrier is congested. Under the queuing operation, the UE is directed to another carrier for a certain time and re-initiates the cell update procedure. The related detailed operation is described as follows. After the UE transmits the CELL UPDATE message after the initiation of the cell update procedure, the UTRAN includes a “Frequency info” IE and a “wait time” IE in the CELL UPDATE CONFIRM message in response to the CELL UPDATE message for indicating the UE to perform the queuing operation. After receiving the CELL UPDATE CONFIRM message, the UE in CELL_PCH state selects a dedicated cell on the new carrier, whereas the UE in the URA_PCH state selects a cell belonging to the dedicated URA. After the cell selection, the UE waits at least the time given by the “wait time” IE, and then reinitiates the cell update procedure.
For a UE not in the queuing operation, a radio link failure, paging response, cell reselection, periodical cell update, an RLC unrecoverable error, and an uplink data transmission may trigger the cell update procedure. However, the prior art does not allow the UE to initiate the cell update procedure during the waiting state if any of the abovementioned events occurs.
When the queuing operation is performed, the UE may switch to another carrier not as congested as the current carrier, and enter the waiting state. There may be a terminating call for the UE during the period of waiting. Since the UE has been directed to the other carrier, the traffic on this carrier is possibly not so congested when the terminating call occurs. Therefore, the carrier should be capable of handling the terminating call for the UE. According to the related specification, the UTRAN accordingly transmits the paging information related to the terminating call to the UE, but the UE cannot respond to the terminating call until the UE leaves the waiting state. Furthermore, the maximum period of the waiting time is 15 seconds. In this situation, the UE may miss the terminating call, since the call connection is delayed.